In situ fluorination of graphite in iron alloy

ABSTRACT

A self lubricating bearing surface is formed on high carbon iron alloy parts by fluorinating the exposed carbon particles at the surface of the part to form carbon monofluoride. The part is fluorinated in a reaction chamber by exposure to fluorine gas not exceeding a partial pressure of 76 torr in an inert gas and a temperature not exceeding 700* centigrade to substantially completely convert all exposed carbon particles to carbon monofluoride.

United States Patent 1 1 1 3,765,929 Martin Oct. 16, 1973 4] IN SITUFLUORINATION 0F GRAPHITE IN 3,567,521 3/1971 Toy et al 117/106 R IRONALLOY 3,607,747 9/1971 lshikawa 252/12 Inventor: Jerry Thomas Martin,Plainview,

Minn.

Assignee: International Business Machines Corporation, Armonk, NY.

Filed: Mar. 31, 1972 Appl. No.: 240,268

References Cited UNITED STATES PATENTS 5/1963 Kanter 117/75 PrimaryExaminer-Murray Katz Assistant Examiner-Dennis C. KonopackiAttorney-Robert W. Lahtinen et a1.

ABSTRACT 10 Claims, No Drawings IN SITU FLUORINATION OF GRAPHITE IN IRONALLOY BACKGROUND OF THE INVENTION This invention pertains to bearingsand more particularly to creating self-lubricating bearing surfaces atthe surface of high carbon alloy iron materials by fluorinating thecarbon particles exposed at the surface to form carbon monofluoride.

Many plating and other surfacing techniques are utilized to enhance thewear and lubricating qualities of bearing surfaces. In the method of thepresent invention a self-lubricating bearing surface is created at thesurface of high carbon alloy materials such as cast iron having freecarbon particles exposed, by reacting such carbon particles to formcarbon monofluoride.

The present invention provides a self-lubricating bearing on a cast ironsurface by converting the exposed particles of free carbon to carbonmonofluoride. A part formed of high carbon iron alloy is machined to adesired dimension with an allowance for a slight growth of the carbonparticles along the surface during the fluorination process. Thiscompensation is necessary to avoid any post fluorination surfacetreatment that would involve material removal. The resulting surface isa machined cast iron surface with exposed particles of carbonmonofluoride that project a few ten thousandths of an inch from thesurrounding iron matrix and form the self-lubricating bearing surface.

DESCRIPTION The surface of a high carbon iron alloy to be treated isprepared by machining the surface with accommodation for material growthwhere appropriate. For example, it is has been found necessary whenpracticing the present invention to oversize a bore by 0.0005 of an inchto accommodate the material growth during the conversion of carbon tocarbon monofluoride.

The prepared part is placed in a nickel or nickel lined chamber for thefluorination process. On the first occasion that fluoride gas isintroduced into the chamber, the fluoride promptly forms a film ofnickel fluoride along the surface of the chamber which is adherent,invisible and which precludes further reaction between the nickelsurface and the fluorine gas.

The chamber is thereupon purged of oxygen and moisture by theintroduction of an inert gas such as helium or nitrogen. The chamber isalso slowly heated simultaneously with the purge to a temperatureusually not exceeding 200 centigrade to assure that any moisture isvaporized and removed from the chamber. When the purge is complete,fluorine gas is introduced as a partial pressure in an inert gas such ashelium or nitrogen. To control the reaction, causing carbon to beconverted to carbon monofluoride while not reacting with the iron, theconcentration of fluorine in the inert gas (at atmospheric pressures) isnot allowed to exceed a per cent partial pressure and the usual practiceis to use a partial pressure in the range of 3 to 4 percent or a partialpressure of about 25 torr. During fluorination, the temperature iselevated to a value not exceeding 700 centigrade. The temperaturelimitation likewise is imposed to assure that the fluorine will reactselectively with the carbon particles and to the exclusion of the iron.

The fluorination process is continued until the exposed graphite orcarbon particles resident at the surface are converted to carbonmonofluoride. When the process has been completed, the part is removedfrom the chamber and rinsed in a mild alkaline solution to neutralizeany hydrofluoric acid that might be resident on the surface and isthereafter dried by exposure to a forced flow of air. To preventdegradation of the surface during subsequent shipment or prior toassembly, the part is dipped in a water replacing oil to remove anyresidual moisture.

EXAMPLE 1 A high carbon alloy sample is placed in a 1,000 cc nickellined reaction chamber. The chamber is thereupon purged with helium atthe rate of 50 ccs per minute for a period of 1 hour to remove moistureand oxygen while slowly heating the chamber to 200 centigrade. Fluorineis thereafter introduced into the chamber at a partial pressure of 25torr in helium at a rate of 50 cc of the gas mixture per minute and thetemperature is simultaneously gradually raised to 640 C. Then theintroduction of the gas mixture is continued for a period of l hour,while maintaining the reaction chamber at a temperature of 640centigrade. The sample is then removed and rinsed in a mildly alkalinewater solution to neutralize any HF present and thereafter dried inblowing air. The sample is finally dipped in a water replacing oil inpreparation for storage and shipment.

EXAMPLE 2 A high carbon iron alloy sample with exposed particles at thesurface is placed in a 1,000 cc nickel lined reaction chamber. Thechamber is thereafter purged with nitrogen at the rate of 50 ccs perminute for a period of 1 hour to remove moisture and oxygen while slowlyheating the chamber to 200 centigrade. Fluorine is then introduced intothe chamber at a partial pressure of 25 torr in nitrogen at a rate of 50cc of the gas mixture per minute while simultaneously, gradually raisingthe chamber temperature to 640 C. Thereafter the introduction of the gasmixture is continued for a period of 1 hour while maintaining thereaction chamber at 640 centrigrade. The sample is then removed andrinsed in a mildly alkaline water solution to neutralize any HF presentand thereafter dried in blowing air. The sample is thereupon treatedwith a water replacing oil in preparation for storage and shipment.

EXAMPLE 3 A high carbon iron alloy sample is placed in a 1,000 cc nickellined reaction chamber. The chamber is then purged by the introductionof helium at the rate of 50 ccs per minute for a period of 1 hour toremove moisture and oxygen while slowly heating the chamber to 200centigrade. Fluorine is thereupon introduced into the chamber at apartial pressure of 25 torr in helium at the rate of 50 cc per minutewhile simultaneously, gradually raising the reaction chamber temperatureto 400C. Thereafter the introduction of the gas mixture is continued fora period of 4 hours while maintaining the reaction chamber at atemperature of 400 centigrade. The sample is then removed and rinsed ina mildly alkaline solution to neutralize any HF present and thereafterdried in blowing air. The sample is Finally dipped in a water replacingoil in preparation for shipment.

In addition to materials such as cast iron, selflubricating bearingsurfaces may be formed on other parts composed of iron and presentingfree carbon particles at the surface in accordance with the abovedescribed technique. By way of example, powdered metal parts whichpossess free carbon particles could be similarly treated.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. The method of forming a self-lubricating bearing surface on a highcarbon iron alloy part comprising placing said part in a reactionchamber which is resistant to reaction with fluorine gas; purging saidreaction chamber with an inert gas to remove substantially all moistureand oxygen; and introducing fluorine gas at a partial pressure notexceeding 76 torr in an inert gas while maintaining said chamber at atemperature not exceeding 700 centigrade until the exposed carbonparticles at the surface of said part are substantially completelyconverted to carbon monofluoride.

2. The method of claim 1 further comprising slowly heating said chamberto a temperature in excess of 100 centigrade during said purging step toinduce vaporization of moisture.

3. The method of claim 2 wherein the inert gas utilized during saidpurging and fluorinating steps is helium.

4. The method of claim 2 wherein the inert gas utilized during saidpurging and fluorinating steps is nitrogen.

5. The method of claim 2 further comprising the step of rinsing saidpart in a mild alkaline solution after said carbon particles exposed atthe part surface have been substantially completely converted to carbonmonofluoride. a

6. The method of claim 5 further comprising the step of drying said partfollowing the rinsing thereof and applying a water replacing oil to thesurface thereof.

7. The method of claim 6 wherein said reaction chamber has a nickelsurface which develops a reaction resistant nickel fluoride film thereonin the presence of fluorine gas.

8. The method of forming a self-lubricating bearing surface on a highcarbon iron alloy part comprising placing said part in a reactionchamber that is resistant to fluorine gas; purging said reaction chamberwith an inert gas while slowly raising the temperature of said chamberto an excess of centigrade to remove substantially all moisture andoxygen therefrom; and introducing fluorine gas at a partial pressure notexceeding 10 percent of the total pressure in an inert gas into saidreaction chamber while not exceeding a temperature 700 centigrade untilthe carbon particles exposed at the surface of said part aresubstantially completely converted to carbon monofluoride.

9. The method of claim 8 wherein said inert gas is helium.

10. The method of claim 8 wherein said inert gas is nitrogen.

2. The method of claim 1 further comprising slowly heating said chamberto a temperature in excess of 100* centigrade during said purging stepto induce vaporization of moisture.
 3. The method of claim 2 wherein theinert gas utilized during said purging and fluorinating steps is helium.4. The method of claim 2 wherein the inert gas utilized during saidpurging and fluorinating steps is nitrogen.
 5. The method of claim 2further comprising the step of rinsing said part in a mild alkalinesolution after said carbon particles exposed at the part surface havebeen substantially completely converted to carbon monofluoride.
 6. Themethod of claim 5 further comprising the step of drying said partfollowing the rinsing thereof and applying a water replacing oil to thesurface thereof.
 7. The method of claim 6 wherein said reaction chamberhas a nickel surface which develops a reaction resistant nickel fluoridefilm thereon in the presence of fluorine gas.
 8. The method of forming aself-lubricating bearing surface on a high carbon iron alloy partcomprising placing said part in a reaction chamber that is resistant tofluorine gas; purging said reaction chamber with an inert gas whileslowly raising the temperature of said chamber to an excess of 100*centigrade to remove substantially all moisture and oxygen therefrom;and introducing fluorine gas at a partial pressure not exceeding 10percent of the total pressure in an inert gas into said reaction chamberwhile not exceeding a temperature of 700* centigrade until the carbonparticles exposed at the surface of said part are substantiallycompletely converted to carbon monofluoride.
 9. The method of claim 8wherein said inert gas is helium.
 10. The method of claim 8 wherein saidinert gas is nitrogen.